The invention relates to a charge-coupled device having a semiconductor body comprising at least two charge transport channels, which are defined at a surface, are located beside each other and have parallel charge transport directions and rows of clock electrodes provided on the surface and extending in the longitudinal direction of the charge transport channels for applying clock voltages for controllably storing information representing charge packets in charge storage regions in the charge transport channels and for transporting charge packets from one charge storage region to a next charge storage region, while between the two charge transport channels at least one connection channel is formed, which is limited by channel-limiting regions and through which charge packets can be transferred from one charge storage region in the first charge transport channel to the second charge transport channel.
This device can form part of the horizontal read-out register of a bidimensional charge-coupled image sensor arrangement, for which the invention is of particular importance. These image sensor arrangements comprise a system of vertical charge transport channels, through which charge packets representing image information are transported in parallel in lines to the read-out register. The charge packets are introduced in parallel into the horizontal read-out register in a linewise manner and are then transported through the horizontal read-out register, at whose output they can be read out in series. As is known, preferably two or three adjacent charge transport channels are provided for the horizontal read-out register, the charge packets of an image line being distributed over these two or three transport channels before they are transported to the output. Such an arrangement is known inter alia from the article "High Density Frame Transfer Image Sensor" of Beck et al, published in "Proceedings of the Fourteenth Conference on Solid State Devices", Tokyo 1982, Japanese Journal of Appl. Phys., Vol. 22, (1983), Suppl. 22-1, pp. 109/112. FIG. 5 of this publication shows a horizontal read-out register having three parallel channels.
A charge-coupled device of the kind described above having at least two adjacent charge transport channels and at least one connection channel between these channels can be used not only in bidimensional image sensors, but also in other types of devices, such as, for example, in line sensors. This type of sensor, which may be used, for example, for facsimile applications, essentially comprises one single line of photosensitive elements or pixels. Two (or more) charge transport channels can be provided on either side of the line for reading-out purposes. The pitch between the pixels can then be four times the pitch of the bits in the charge-coupled device, which is often desirable in connection with the resolving power. A charge-coupled device of the kind described above can be used in arrangements only intended for signal processing purposes. Although the invention will be described especially with reference to bidimensional image sensors, it should therefore be taken into account that the invention is not limited to this type of arrangements.
In image sensors of the kind described inter alia in the aforementioned publication, a line of charge packets corresponding to the line pixels of, for example, a T.V. display apparatus is introduced from a memory into the horizontal read-out register. The period of time required for transferring from the parallel section to the horizontal read-out register and for distributing the charge packets over the three horizontal channels is determined by the line fly-back time, which is, for example, 12 .mu.sec.
It has been found in practice that the distribution of the charge packets over the three horizontal channels is a very critical operation and that at least with the use of the normal clock voltages the period of the line fly-back time is too short, as a result of which the transport efficiency is too low due to the fact that charge is left.